Spark gap constructions



March 8, 1960 F. .1. scHuL'rz 2,928,017

' SPARK GAP coNsTRUcTroNs Filed June 9, 1958 AYIAWIIIY lNVENTOR FRED J. ScHuL'rz BY Afronnex mit@ SPARK GAP coNsTRUc'iioNs Application June 9, 19158, Serial No. 740,643 ys claims.' (ci. 31a- 231) This invention relates to spark gap constructions.

Although spark gap Vconstructions can be used in a number of places theyare primarily intended for use in a lightning arrester. In oneV type of lightning arrester it is the usual practice to use some form of spark gap in combination with so called valve material to make what is commonly referred to as a valve type lightning arrester.

Under normal conditions the main purpose of a spark gap in a -valve type lightning arrester is to isolate the live line from ground. When a high voltage surge occurs the gap sparks over permitting a quick by-pass of the surge current to ground. This spark over of the spark gap by surge, however, generally also initiates power follow current to ground. It is desirable to interrupt the power Vfollow current ow as soon as possible. Therefore, it is preferred that the same spark gap' interrupt the power follow current to restore the line to its original normal operating condition as soon as possible. Thus the object of any spark gap design is to keep the surge spark over value caused by a lightning strokeor the like as low as is practically possible to give the best protective characteristic and yet maintain proper line voltage isolation relative to ground to prevent dissipation of generated current and also provide quick interruption of the power follow current through the arrester after sparkover of the spark gaps by a surge. v a The main purpose of the -valve material is to provide a low impedance' to the 'passage of surge currents and a high impedance to power follow current thus limiting the value of power follow current to a level which the associated spark gap Vcan .successfully interrupt.

The spark gaps heretofore in use have beenrof two main types, namely, a ladderigap wherein spaced metallic electrodes are disposed in electrical series arrangement as shown, for example, in Patent No. 2,165,964, of July 11,1939, for lightning arresterl issued to R. H. Earle et al."and assigned to the same assignee as this application, or of the magnetic type wherein the arc is stretched or extended away from the closest point between-spaced electrodes by external magnetic means.l

It is an object of this invention to provide a compact magneticpspark gap for lightning arresters wherein the arc movement is accomplished by the inherentmagnetic eld provided bythe mechanical construction or by the use of anexternal magnetic coil operating in conjunction with Yand supplementing` this inherent` magnetic field. Such a gap construction provides the ability to interrupt the high follow currents usually associated with the low discharge voltage or `IR drop characteristics needed formodern'valve type lightning arresters.

Furtherspeciiic `objects of this invention are to pro-` Baented Mar. 8, `196() gap construction in whichthe arcrotates about a central electrode on the one hand and along a spiral electrode on the other hand andi in which the arc is forced to rotate inthe same direction that the expanding spiral elecby the conducting spiral electrode 15.

trode is wound, thereby causing a continuous and relatively rapid llengthening of the arc itself and preventing the arc from iumping from one convolution to the other.

Embodiments of the invention are shown in the accompanying drawings in which:

' Figure 1 is a view partly broken away and partly in section showing the spark gap in the position it occupies in .the Ylightning arrester.

Figure 2 is a sectional view through the spark gap construction. v

y 'Figure is a sectional view on the line 3-3 of Figure 2.

Figure 4 is a sectional View corresponding to Figure 2 and showing a further form of spark gap construction.

Figure 5 is a sectional view on the line 5-5 of Figure 4.

Referring to the drawings, particularly Figures 1, 2 and 3,`it will be seen that the lightning arrester comprises a housing or casing 1 of insulating material such as porcelain or other suitable insulating material. Valve material 2 such as silicon carbide is carried in the lower portion of the housing 1 and separated from the upper portion of the lightning arrester by the metal plate 4.; The spark gap construction 3l is located above the valve material and has a lower contact member such as the metal plate 10 resting upon the metal plate 4. The upper portion of the lightning arrester has a conducting plate or cap 5 spun in place, gaskets 6 being-interposed between this upper metal cap 5 and the casing 1. A suitable,y small plastic housing 7 surmounts the lightning arrester. The space between the small housing 7 and the adjacent portion of the arrester is lled with insulating material 8', as in the usual constructions. The metal cap 5 is soldered, brazed or otherwise secured to the live, or line conductor 8, the lower grounded conductor being indicated at 9.

This general type of construction'is shown in the patents to Ralph H. EarleNo. 2,296,708 of September 22, 1942, forv Circuit Interrupting Device, and 2,315,320 of March 30, 1943, for Automatic Circuit Interrupting Device, both assigned to the same assignee as the present invention.

The spark gap construction, indicated generally at 3, is provided with the lower metal plate 10 hereinabove mentioned, and an upper metal plate 11. A ilexible conductor 12lsuch as braided metal, spring pressed by the spring 13, connects the upper metal plate or terminal member 11 of the spark gap construction with the upper metal cap S of the lightning arrester.

Attention is now directed to Figures 2 and 3. The spark gap construction 3 includes a casing or body portion 1'4 of'plastic or other insulating material which car-j ries withinitself an upwardly expanding spiral conductorY or electrode 15 seated in depressions 16 arranged in a stepped manner in the casing 14 of the spark gap con struction. This insulating casing 14 or body vportion yof the spark gap construction is provided with an upwardly extending integral stud 17, as shown in Figures 2 and 3, which enters the metal cylindrical member or central electrode 18. The central electrode 18 s'surrounded The' -electrodea and 18 and their metal plates 10 and 11, respectively, constitute the two terminal portions of the spark gap construction. The member 18 is connected to, and supported by, the upper metal plate 11. The metal plate 11 is covered on its under side by an insulating disk 19 which rests on spaced projections 20 formed integrally with the upwardly projecting marginal Vportion of the insulating casing or housing 14 ofthe spark gap Vconstruction as shown in Figure 3. The lower plate iii is provided with an aperture which receives acentrally located projection 21"of the casing or body portion i4. The lower end of the conducting spiral 15 is ,electrically connected to the lower metal platetl as shown in Figure 2. It is to be noted from Figures 2 and 3 that a series of vents 21 are provided in the body portion 14.

The operation ofthe apparatus is as follows:

When a lightning surge occurs an arc is formed between the conducting spiral or electrode 15 and the central electrode 18. The current therefore passes as a substantially radially positioned arc from the central electrode l to the spiral 15, or vice versa. The current then continues in a spiral path around the central conductor or lelectrode 1S and thus produces a vertical llux through the spiral electrode 15. The spiral 15 is wound in such a direction that the are is forced to rotate or sweep around the central electrode 18 and to thus follow the upwardly expanding spiral 15. The direction in which the arc rotates is the direction in which the spiral 15 is wound. ln other words, the direction of the rotation of the arc is the same as the direction in which the spiral is wound irrespective of the direction of the surge downwardly through the spark gap construction or upwardly through the spark gap construction. It will be seen that the arc is caused to rotate and follow the spiral 15 in such a direction, as stated above, that the arc is continually elongated due to the expanding spiral. ln addition to this, the arc constantly travels along relatively cool new portions of the spiral '15. These two effects, viz., the gradual extension or lengthening of the arc, and the contact of the arc with new, relatively cool metal, serve to quickly extinguish the arc.

A series of vents 21 are formed in the upper circular margin of the body portion.

ln order to increase the tlux through the conducting spiral, an auxiliary coil may be added, as shown in Figure 4, and this auxiliary coil is connected in series with the spiral electrode. This increases the flux through the spiral and thereby increases the force acting on the arc producing its rotary motion.

Referring to Figures 4 and 5 it will be seen that the spark gap vconstruction is provided with `a body portion 23 of suitable insulating material in which is located a central electrode 24 and the spiral electrode 25. .The

spiral is connected at its lower end to a lower or intermediate metal plate 26 which lower plate has a depressed portion spaced a small distance, as indicated at 27, from the bottom metal plate 28. The upper conducting plate or terminal is indicated at 29 and is spaced from the remainder of the spark gap construction by means of an insulating disk 30. Vents 31 are provided as previously described.

The bottom or lower metal plate or terminal 28 is spaced from the lower, intermediate metal plate 26 and between these plates a small auxiliary spark gap or space 27 is provided. rl`he lower end of the spiral 25 is electricaly connected to the intermediate lower metal plate 26. An auxiliary coil 32. is wound around the main body or insulating casing Z3 of the spark gap and is positioned within an annular groove 33. The direction of winding, or in other words, the direction of current flow in the coil 32 is the same as the direction of current ow in l the spiral 25 and thus increases the flux through the spiral.

The terminals of the coil E?. are connected respectively to the intermediate plate26 and the lower `plate 28 and the coil is connected in series through the plate 26 to the spiral electrode 25. The lower plate 2S and the intermediate plate 26 are spaced apart by means of insulating spacers 3'4, as shown in Figure 4. The conductors connecting the ends of the coil with the two electrodes or plates 26 and 23 of the auxiliary spark gap 27 are indicated at 35 and 36 in Figures 4 and 5.

The operation of the last described form of the invention shown in Figures 4 and 5 is the same as that outlined for the rst form of the invention shown in Figures 2 and 3, except for the coil 32 and the auxiliary gap 27. lt is to be noted that the small spark gap 27 is a protective gap bridged across the coil 32 'and thus protecting the coil against excessive voltage.

It will be seen that this invention provides a spark gap construction in which the arc is caused to rotate and pass continuously from a relatively small diameter portion of an expanding spiral electrode, along the spiral elec trode, to a relatively larger diameter portion, and to thus continuously lengthen and continuously shift to a new cool surface.

The expressions upper and lower, or upwardly and downwardly, are used merely for the purpose of simplitying and shortening the description of the spark gap constructions and claims therefor, `and are not intended as limiting expressions asthe spark gap constructions and, in fact, the complete lightning arrester may be mounted in any manner desired.

Although the invention has been described in considerable detail it is to be understood that such description is intended as illustrative and not as limiting as the invention may be variously embodied and is to be interpreted as claimed.

l claim:

l. A spark gap construction comprising an upper contact member and a lower contact member, an insulating housing open at the top and positioned between the upper and lower contact members, a centrally located electrode connected to the upper contact member, a spiral electrode surrounding the central electrode and spaced therefrom and secured at one end ofthe lspiral electrode to the lower contact member, said centrally located electrode and said spiral electrode constituting the main spark gap across which an arc is formed in a normal operation of the spark gap, the spiral electrode being wound in a direction to produce a magnetic field therethrough in a direction to cause an arc between the central electrode and the spiral electrode to rotate in a direction so that the arc advances upwardly of the spiral electrode, said spiral electrode terminating at its upper end out of contact with the contact members.

2. A spark gap construction,comprisingV an upper contact member and a lower contact member, a central electrode connected to the upper contact member, an expanding spiral electrode having an unconnected upper end and having a lower end connected to the lower contact member and surrounding the central electrode, said central electrode and said spiral electrode constituting the main spark gap across which an arc is formed in the normal operation of the spark gap, an inulating body portion positioned between the upper and lower contact members, the spiral electrode being wound in such a direction that the magnetic field therethrough when an arc is formed between the central electrode and the spiral electrode will be in a direction to cause the arc to rotate in a direction to follow the spiral electrode irrespective of the direction of the current passing through the spark gap, whereby the arc is caused to rotate in a gradually advancing manner between the central electrode and the spiral electrodetowards the unconnected end thereof.

3. A spark gap construction comprising an upper and a lower contact member, an insulating body portion between the upper and lower contact members, a central electrode extending downwardly from `the upper contact member, `a spiral electrode surrounding the central electrode and expanding upwardly and having its lower end connected to the lower contact member and havingits upper end free of connection to any conducting portion of the spark gap construction, said central electrode and said spiral electrode constituting the main spark gap across which an arc is formed in the normal operation of the spark gap, and a coil surrounding the spiral electrode and augmenting the flux produced by current owing through the spiral electrode when an are -is struck between the central electrode and the spiral electrode, the iiux being in a direction to cause the arc to advance valong the spiral electrode from its lower end to its upper end, said coil being connected in series with the spiral electrode between the lower contactkmember and the upper contact member.

4. A spark gap construction comprising an upper eontact member and a lower contact member, a central and a spiral electrode forming the main spark gap across which an arc is formed in the normal operation of the spark gap, an insulating body portion positioned between the upper and lower contact members and supporting said spiral electrode in spaced relation to,l and surrounding, said central electrode, a coil, and an auxiliary spark gap bridging said coil, said coil being wound in a direction to supplement the magnetic ux produced when current ows through the spiral electrode and through the coil. l

5. A spark gap construction comprising an upper cony tact member and a lower tcontact member, a central and a spiral electrode, an insulating body portion positioned .between the upper and lower contact members and supporting the spiral electrode in spaced relation to and surrounding the central electrode, said central and spiral electrodes constituting a main spark gap across which an are is formed in the normal operation of the spark gap,

a coil, andan auxiliary spark gap, said ,auxiliary spark Y References Cited in the le of this patent UNITED STATES PATENTS Y 2,512,301 y Brees@ June 20,1950

2,573,005v f oiypns oct. so, 195i Cook r Oct. 23, 1956 

